In known radio base stations for cellular telephony networks, there is a number of so called radio chains, each radio chain comprising a power amplifier, which may itself be comprised of a number of amplifiers which are connected so as to have a common input port and a common output port. Each radio chain will typically also comprise one or more antenna elements, which may be a part of a larger antenna with more antenna elements, such as an electrically steerable array antenna.
In future radio base stations, it would be an advantage if the stations could support both so called BF-transmission (beam forming), where typically one data stream is transmitted to each user, as well as so called MIMO-transmissions (Multiple Input, Multiple Output), where a plurality of data streams are transmitted to each user.
The antenna requirements for BF-transmissions are quite different from those of MIMO-transmissions, so a conventional way of designing a radio base station which would be capable of both would be to have separate antennas for each case, as well as separate radio chains for each antenna or a switching device between the power amplifier resource and the antennas.
Since MIMO and BF would typically not be used simultaneously, this design would lead to a radio base station with poor usage of power amplification resources, as well as a radio base station with quite voluminous equipment, neither of which is desirable.